The present invention relates to a display system comprising a substantially flat matrix display panel producing a display output.
Flat panel matrix display panels such as liquid crystal display devices (LCDs) are now commonly used as alternatives to traditional CRTs (Cathode Ray Tubes) in many different display applications where, for example, their relative compactness and their flat viewing surface offer advantages over CRTs. However, while these attributes make them particularly attractive for a range of display purposes, there can be situations where, for example, for ergonomic design, aesthetic or other like reasons, it would be useful for the LCD panel""s viewing surface to be curved rather than flat. Examples of such applications could include stylised television receivers using unconventional cabinet shapes, portable display equipment, children""s toys, and displays in vehicles. For instance, it is known to incorporate LC display panels vehicle dashboards as information displays and in the back of headrests in vehicle seats for video display purposes and it would be beneficial if the display viewing surface were curved so as to conform with the dashboard or head rest contours and present a continuous curved surface flush with the surrounding structure. If the display panel were simply recessed and a curved transparent window placed thereover, there is a tendency for a viewer to focus on the window rather than the display panel which leads to viewing difficulties. As yet, flexible LCD panels using plastics substrates rather than the conventional glass substrates and suitable for these kinds of applications are not commercially viable.
It is known to project the display output of an LCD panel by means of a projection lens enlarged onto a curved projection screen. Such a system may be used as a wide angle LC projection system suitable for specific purposes such as gaming or audioxe2x80x94visual entertainment and enabling a viewer to be partially surrounded by the enlarged display image. However, such a system is totally unsuitable for normal display applications in which display images corresponding approximately to the size of the pixel array of the display panel are required.
According to the present invention, there is provided a display system comprising a substantially flat matrix display panel, a curved viewing screen arranged over, and spaced from, the output side of the panel and an optical image transfer arrangement disposed between the curved screen and the output side of the panel and comprising at least one microlens array which is curved in the same general direction as the screen and which has spaced apart lens elements for transmitting respective portions of the image produced at the output side of the panel onto corresponding positions on the curved screen. Through such image transfer arrangement, the image produced by the panel is relayed in simple manner to a curved viewing screen, for example curved to present a continuous surface conforming to, and flush with, the surface contour of a surrounding structure. Importantly, the required microlens array occupies little space so a compact arrangement is obtained. This makes it possible to achieve the desired object in a space saving manner and with the image produced on the viewing screen being of similar dimensions to that produced by the panel.
The matrix display panel preferably comprises an LCD although other types of substantially flat display panels such as electroluminescent, field emission, and electrochromic display panels could be used instead.
The viewing screen may be curved in one or more directions. As simple examples, the screen may be of a part cylindrical, barrel, or spherical form. By suitable microlens array design the desired image shape, conforming with such types of curvature, can be conveniently obtained in relatively simple manner. While the array is curved in the same general sense as the screen, its curvature does not have to correspond. The microlens array is curved such that its spacing from the panel varies over its area in similar manner to the curvature of the viewing screen. By changing the spacings between the microlens array and the panel over its area the object and image distances in the arrangement are varied and this effect is utilised to re-image the display produced by the panel onto the curved viewing screen such that the object to image distances obtained are varied in corresponding manner to conform with the curvature of the viewing screen. For optimal imaging, preferably there is a variation in the powers of individual lens elements over the area of an array as well as curving of an array, such variation being either in the curved array and/or one of the other arrays. As mentioned, the viewing screen may be curved in one or more dimensions. As well as having a generally symmetrical form, for example, part cylindrical shape, non-symmetrical curvatures are also easily possible.
Although a single microlens array may be adequate in certain circumstances, for example, where each display pixel (e.g. colour triplet) of the display panel is associated with a respective lens element of the array, the image transfer arrangement preferably comprises a plurality of microlens arrays, each having spaced apart lens elements, with corresponding lens elements in the arrays being optically associated with one another. Such an arrangement can enable an individual lens element to be larger and associated with a group of adjacent display pixels. Alternatively, in the case where a first array has a respective lens element for each display pixel, a second array comprising field lenses may be used to improve optical performance.
In a preferred embodiment, the image transfer arrangement comprises, in order from the panel, a first, imaging, microlens array, a second, field, microlens array and a third, re-imaging, microlens array, the first, second and third microlens arrays being arranged such that each microlens element in one array is on the same optical axis as a corresponding microlens elements in each of the other arrays and with each group of corresponding microlenses elements relaying a respective portion of the image to the viewing screen. Such a microlens system enables the image produced on the panel to be relayed in a non-inverted manner onto the viewing screen. Each group of microlens elements can then work with a large area of the display comprising multiple pixels, for example between 10 and 100 colour triplets. Only one of the arrays need be curved. Preferably, the powers of the microlenses elements in one or more of the arrays are varied over the area of the array according to the curvature of the screen so that the display output is correctly re-imaged on the curved screen.
By forming the curved microlens array as a sheet using a plastics material the required curving can be obtained relatively easily. Where curving in a single dimension is required, the sheet may be simply bent. Where curving in two dimensions is required the sheet can readily be moulded appropriately in that shape. If the power of individual microlens elements in an array are to vary in accordance with the curvature of the viewing screen, then different radii or different refractive indices can be used.
In order to avoid or reduce optical crosstalk, and improve efficiency, light baffle means may be provided adjacent at least one of the arrays, preferably the first array, so as to prevent light reaching a microlens element other than from the intended direction. In a particularly preferable arrangement, the light baffle means are provided between the first and second arrays. Such light baffle means for example, may be provided conveniently in the form of a honeycomb structure disposed in front of the first array or between the first and second arrays. In addition, a further microlens array comprising field microlens elements, each corresponding to, and arranged on the same optical axis as, a respective microlens element in the first array may be provided close to, and preferably directly on, the output side of the panel to improve light utilisation.